The present invention is generally related to a probe interface assembly, and, more particularly, to a compliant probe interface assembly for imaging breast tissue with an ultrasound probe in conjunction with X-ray mammography, thereby providing geometrically registered X-ray and ultrasound images.
FIG. 1 illustrates a schematic of conventional X-ray mammographic equipment combined with an ultrasound scanning system. This usually includes a compression plate 10 (e.g., a plate made up of polycarbonate such as Lexan or other suitable materials) to compress and flatten breast tissue 12 against a detector plate 18. In order to perform an ultrasound scan subsequent to an X-ray mammogram, the system further includes an ultrasound probe 14, as may be positioned to traverse atop such a plate to generate ultrasonic images of the internal structure of the breast tissue. A gel 16 may be provided as shown in FIG. 1. The gel typically comprises a suitable composition for reducing acoustic impedance mismatch and reflectance at the plate/probe interface. Ideally, the compression action should provide uniform contact of the breast tissue with the compression plate to achieve appropriate ultrasound propagation as well as superior X-ray imaging.
In practice, the compressing surface of the compression plate may deform when exposed to typical mammographic breast compression forces. The resulting maximum deflection of the plate, as may be measured from a horizontal plane, should be typically constrained to lie within 1 cm, as per MQSA requirements. Since the ultrasound probe 14 rides on top of this deformed plate, as shown in FIG. 1, the ultrasonic beam propagates through a non-uniform gap and a non-parallel surface.
A varying gap changes the ultrasound path between the probe and the compression plate and leads to inconsistent attenuation. A non-parallel surface may lead to variable beam refraction, as the ultrasound beam may be formed from multiple elements in a linear array ultrasound probe. Each of these conditions could have adverse effects on the ultrasound image quality. These conditions may also make it burdensome for a radiologist to correlate an X-ray image to an ultrasound image due to the lack of a consistently reproducible setup from one scan to the next scan.
A thicker plastic plate or a metallic plate would reduce the deflections but would have detrimental effects on ultrasound and x-ray image quality. A relatively thin compression member would reduce ultrasound attenuation. However, a thinner compression member by itself is not a viable solution since a thinner member would have excessive deformation resulting in a non-planar scan surface for the ultrasound probe. In one known compression member, use of a 1 mil (0.025 mm) thick Kapton plate typically results in deformations far exceeding 1 cm when subjected to maximum compression loads of 20 dekanewtons (dkN). Also a non-planar surface, resulting from the usage of a thin membrane, is not easily amenable to automated ultrasound scan. Image reconstruction also becomes complicated and would require processing additional information such as probe orientation relative to scan surface.